1. Field of the Invention
The present invention relates to a torch cable accommodating structure in an industrial robot mounted with a torch for arc welding.
2. Description of the Related Art
As one of typical applications of a robot, there is an arc welding robot. The arc welding robot is an industrial robot which has a torch for arc welding (hereinafter, referred to as “a welding torch” simply) mounted in the vicinity of a distal end of an arm thereof for performing an arc welding on a workpiece.
In an actual working site using an arc welding robot, there may by a case where a welding workpiece must be conducted in a state where an arm of the arc welding robot has been inserted in a narrow space such as a space in a workpiece, a space in a jig or a space in a peripheral device. In such a case, a problem of interference tends to occur in association with movement of the arc welding robot. In particularly, a torch cable connected to a welding torch has a high possibility that it interferes with a workpiece, a jig or a peripheral device in the vicinity of the torch cable, as compared with the distal end portion of a robot arm or the welding torch moving in a relatively narrow range. One of the reasons is that the torch cable is loosely taken about a robot mechanical section in order to secure a feeding stability of the welding wire and an area where the welding cable interferes with the periphery thereof becomes broad correspondingly.
Further, in case where a program for arc welding is prepared in an off-line manner, movement of the arm or the welding torch, an action of a wire feeding apparatus or the like can be simulated but it is difficult to simulate movement of the torch cable between the welding torch and the wire feeding apparatus. This fact is due to such circumstances that a behavior of the torch cable varies largely according to the attitude of axis of a wrist of the robot, the behavior may change with time because of its flexibility and the like. Accordingly, in a stage where the program for arc welding is prepared in off-line, it is not easy to accurately estimate an interference possibility between the torch cable and peripheral objects in advance.
Under these circumstances, there have been several proposals regarding the problem about interference of a torch cable. For example, in Japanese Patent Application Laid-Open No. 09-216189, there is a description about a constitution that a welding torch is provided rotatably about a parallel axis offset from a robot final rotating axis by a predetermined amount and the degree of rotational freedom of the welding torch is increased. Further, in Japanese Utility Model Application Laid-Open No. 05-28563, there has been proposed such a structure as shown in FIGS. 1A and 1B.
As illustrated in FIG. 1A showing a front view of an entire structure, a torch is attached to the distal end of a robot wrist and a wire feeding apparatus which feeds a welding wire to the welding torch via a torch cable is mounted to a supporting base for a robot arm. The wire feeding apparatus can advance and retraction-adjustable (or, is slidable) along the welding wire via a shift unit which is position-controlled by a control section of the robot arm.
In the art described in the above-described Japanese Patent Application Laid-Open No. 09-216189, however, when an attitude of an axis of the robot wrist is changed, as shown by a dotted line in FIG. 1A and FIG. 1B, there is a problem that the behavior of the torch cable changes largely to interfere with the periphery thereof. Further, in the art described in Japanese Utility Model Application Laid-Open No. 05-28563, since a torch cable projects relative to a front arm, there is a high possibility that the cable interferes with the periphery. That is, when the attitude of the welding torch is changed, the welding torch is pivoted relative to the front arm. Therefore, in a case in which the attitude of the welding torch is changed during welding of a workpiece, there may occur a problem of obstructing a welding workpiece such that the torch cable is excessively pulled and twists about the front arm, or the torch cable excessively loosens and its curvature changes largely, which causes inadequate feeding of the welding wire.
Further, when the attitude of the welding torch is changed, there is a problem that the behavior of the torch cable changes largely so that the torch cable interferes with a workpiece, a jig and a peripheral device.